Limnæa has a large flat head, from each side of which issues a triangular contractile tentacle, carrying at its base and on the inner side an extremely small dot, or eye. The most considerable part of the body, comprehending the visceral mass, is spiral, and is contained in a thin diaphanous shell (Fig. 188), the turns in the spiral of which are generally elongated, the last turn being larger than all the others. The interior of this is occupied by the respiratory cavity, which communicates outwardly by an opening analogous to that which exists in the snails. This opening dilates and contracts in such a manner as to receive the air in the cavity, and exclude water when the animal feeds itself under the water. The mouth is a transverse slit between two rather thin lips, and is armed with small canine teeth. When the animal sallies from its shell, it has the appearance of a short trumpet. In its interior is a roundish, thick, and fleshy tubercle, not unlike the tongue of a paroquet. The true tongue, however, which lies at the bottom of the slit, is flat, oval-shaped, and supported by a cartilaginous or bony pedicle.

Limnæa, aided by this very complicated buccal apparatus, is enabled to feed itself with vegetable substances, such as the leaves of aquatic plants, which it cuts and bruises with its teeth. They are very active in the season, reproducing towards the end of spring. At this period little oval or semi-cylindrical masses are frequently found adhering to floating bodies, glittering and transparent as crystal. These are agglomerations of the eggs of Limnæa. When winter sets in, the Limnæa of our climate fall into a state of torpor, and sink, more or less deeply, into the mud of the lakes, marshes, rivers, or brooks, which they inhabit.

They are of great utility, both to feed fishes and aquatic birds, and also as scavengers of the decaying vegetation of brooks.

Planorbis has an organization analogous to Limnæa, of which it is the faithful companion in stagnant waters. Their shells (Fig. 189) are thin, light, and disk-like in form, rolled round its plane in such a manner as to render all the turns of the spiral visible from above as well as below; it is concave on both sides, with an oval, oblong-shaped opening, and with an operculum or lid. The animal is conformable to the shell in shape. The visceral mass forms a very elongated cone, which unwinds itself absolutely, according to the spiral turns of the shell. The foot, or abdominal locomotive mass, is short, and very nearly round. The head is sufficiently distinct, and furnished with two very long filiform, contractile tentacles, having at their base, and on the inner side, a small organ, which looks like an egg. The mouth is armed in the upper part with cross-cutting teeth, and in the lower part with a tongue, bristling with a great number of hooked excrescences.

In habits Planorbis resembles Limnæa: it creeps like it on the surface of solid bodies, and swims in the water with the foot upwards and the shell down. It feeds on similar substances, and its eggs are collected in gelatinous masses also. It passes the winter in a state of torpor, buried in the mud of the rivers it inhabits.

The principal species is Planorbis corneus (Fig. 189) which is common in the rivers of England and France.

Another group of molluscs, which occupy our fresh rivers, and swim with the shell down and feet up, is represented by Physa castanea (Fig. 190). The genus Physa have an oval, oblong, or nearly globular shell, very thin, smooth, and fragile, opening longitudinally, narrow above, with the right edge sharp; the last turn of the spiral being largest of all.

The animal appears to be intermediate in form between Planorbis and Limnæa: it is oval in form, and unrolls itself like the Limnæa, but its tentacles, in place of being triangular and thick like the latter, are elongated and narrow, like those of Planorbis. These little inhabitants of fresh water swim with facility, the feet upwards, the shell below, and like Limnæa, they feed on vegetables.

The fourth family, Limacidæ, containing Testacella and Limax, are terrestrial pulmonary molluscs, entirely naked, or having only a very small shell. The Limax varies very considerably in appearance, in consequence of its extreme contractibility. When seen creeping along on the surface of the soil, it has nearly the form of a very elongated ellipse, at one extremity of which is the head; the surface of the body in contact with the earth is flat, the other convex. Towards the anterior extremity, and upon the middle of the back, a portion of the skin projects as if it were detached from the body, and is ornamented with transverse stripes of various convolutions. This part is named the cuirass, or buckler, under which the animal can hide its head.

The mouth is a transverse opening in the front of the head; above are two pairs of tentacles, or horns, immensely retractile, cylindrical, and terminating in a small button; the lower tentacles are the shorter; the upper present at their summit a black point, as in Helix, which have sometimes been mistaken for the eyes.

Upon the right side of the cuirass, and hollowed in the thickness of its edge, which is large and contractile, whose function it is to give access to atmospheric air, it abuts on an internal cavity, also large, and is intended to promote respiration. The outer skin, or epidermis, is rayed in brownish furrows, its surface covered with a viscous glutinous substance, which permits of the animal creeping up the smoothest surfaces, locomotion being produced by the successive contraction and extension of the muscular fibres of the feet.

The internal organization of the Limax is analogous to that already described in the snails. The taste and smell in the Limaceans differ only very slightly from those organs in Helix. They are, like the snails, deaf, and nearly blind. They love humid places; they lodge themselves in the holes of old walls, under stones, or half-decomposed leaves, in the crevices of the bark of old trees, and even underground, coming forth only at night and in the morning; especially after soft showers in spring and summer. In the garden, after one of these soft showers, many of these little creatures are sure to be met with in the more shaded alleys.

The Limax is mostly herbivorous. They seek, above all, for young plants, fruits, mushrooms, and half-decayed vegetables. They are very voracious, and cause great ravages in gardens and young plantations, and many are the devices of the watchful gardener to destroy them. Lime and salt are their abomination; ashes and fine sand they avoid. They dislike the noonday sun, and the gardener knows it; he arranges little sheltering tiles, or planks of wood and stone, under which they retire, where they are surprised to their destruction.

There are thirty known species of Limax. Some are remarkable for their very striking colours. Limax rufus (Fig. 191) is common in woods, and well known for its large size and its colour of rich yellowish red; it is known all over Europe, from Norway to Spain.

Among the Limaceans nearly destitute of shells we find Testacella haliotidea (Fig. 192), which is provided with a very small shell placed at its posterior extremity, just over the pulmonary cavity. This shell becomes more important in Vitrina, already spoken of as forming the point of transition between Limax and Helix. This passage from Limaceans entirely destitute of shells to those furnished with a very small shell, as in Testacella, is very exactly indicated by Nature. Limax rufus, spoken of above, presents, under the posterior part of the cuirass, calcareous, unequal, isolated granulations, which are, so to speak, the elements, as yet internal, of a shell which is on the point of being built. Other species in the same genus present under the cuirass a little rough, imperfect scale, which seems to be produced by a great number of these calcareous granulations, which show themselves in an isolated state in Limax rufus.

The Helicidæ is the fifth family we shall now consider.

It is only necessary to witness the snail as it creeps along the gravel walks of a garden, or in the damp alleys of a park, in order to see that it is a being of higher organization than the headless molluscs. The common snail (Helix aspersa) goes and comes; it roams and saunters after its own peculiar manner, searching for its food or its pleasure; it has a head and two prominent tentacles, which feel and seem to express their sensations; it has nerves, a brain, a strong mouth, and a well-formed stomach.

Without possessing a high order of intelligence, the snail is by no means imbecile; it knows very well how to choose a tree the fruit of which is agreeable to it. A fine cluster of grapes, a succulent pear, which the horticulturist devours with his looks, and hopes to devour otherwise, is sure to be the identical fruit which will be chosen by our enlightened depredator, the snail.

The body of the snail is oval, elongated, convex above, flat below. The convex or upper surface of the body is rugged, in consequence of the existence of numerous tubercles projecting slightly, and separated by irregular furrows; its anterior is terminated by an obtuse head, its posterior more flat and less pointed. All the flat portion, thick, soft, and upon which the animal moves itself by a creeping motion, bears the name of the foot. The head is not really very distinct, especially in the upper part, but the organs with which it is provided are prominent. These organs are in reality tentacles, although they are more popularly known as horns, especially among children—those charming ignoramuses—who have been taught to repeat the well-known stanza—

which finds its counterpart in all European languages. There are two pair of these tentacles or horns; one pair quite in front and above, and another smaller and less forward. The first are distinguished by their size, and also by a black spot or point at their extremity, which is sometimes erroneously said to be the eye of the snail.

These tentacles differ in many respects from the same organs in other molluscs; they are retractile, and can be drawn altogether within the animal into a sort of sheath, by the contraction of a muscle. At the anterior extremity of the head we find a sort of plaited opening, which is the mouth: it is of moderate extent, closed in front by two lips, and armed with two shear-like organs of horny consistence, one of them being a sort of rasp, which occupies the plate of the buccal cavity, and may be called a tongue; the other is a median jaw, placed transversely in the membranous walls of the palate, terminating in a free edge, armed with small teeth. This cutting blade, however, executes no movement; but the lingual organ, pressing all alimentary matter forcibly against its lower edge, effects their mastication, and enables it to dispose of fruit, tender leaves, mushrooms, and other substances easily divided.

At the bottom of the mouth is an œsophagus, or gullet, to which succeeds a stomach of moderate size. The intestine lies in folds round the liver, which is divided into four lobes, and terminates in a special orifice.

The little lung of the snail is placed in a cavity, vast for its size, just above the general mass of the viscera, and occupies all the last spiral turn of the cavity.

The mechanism of respiration is as follows: The animal inhales the air into its lung by forcibly dilating the pulmonary orifice, which lies in the largest spiral turn of the shell. In order to expel the air respired by the lung, it withdraws its body into the narrower part of the shell, where it gathers itself up completely, even to its head and feet, and by this compression of all its little being it expels the air which fills it. These respiratory movements, however, are not regular, but succeed each other only at certain intervals. Life would be too hard for the poor snail were it passed in such violent efforts as would be necessary if it respired as the larger animals do. In its case the breathing is intermittent and imperfect; it is merely a rough attempt, as it were, at respiration, which becomes perfect in some of the higher branches of the animal kingdom.

The snail has a heart, consisting of a ventricle and auricle, connected with a well-developed arterial vascular system, while the venous system is imperfect. In short, the blood only returns from the various parts of the body to the respiratory apparatus, after traversing lacunæ, or air-cells, existing between the several organs.

The blood of the snail is of a pale rose colour, slightly tinted with blue. It has a rudimentary brain, composed of a pair of thick ganglions, situated above the œsophagus, which are in connection with another pair of ganglions placed below, which, together, form a sort of collar, or ring. From this ring springs a great number of nervous cords, which are distributed to the mouth, the tentacles, the lung, and the heart. The skin, in those parts covered by the shell, exhibits great sensibility; it receives a considerable quantity of nervous filament, so that the sense of touch ought to possess extreme delicacy.

The tentacles, the skin of which is so fine and so sensitive, are the organs of touch. Other functions are sometimes attributed to them; the anterior tentacles are sometimes considered to be the organs of smell. This, at all events, is certain, that the snail is very sensible of strong odours, and is easily attracted by many plants the odour of which pleases it.

The black points which terminate the first pair of tentacles have been considered as eyes: but the existence of a visual organ in the snail is not quite certain. They are quite insensible to sudden changes of light; they always travel in the dark, and never recognize obstacles placed before them. We may add that the snail is destitute of all organs of hearing. No noise appears to affect it, at least till the noise is so near as to agitate the air which immediately surrounds it. Indeed, the snail few has senses; the poor creature is at once blind, deaf, and dumb.

The snails are male and female in the same individual, or hermaphrodite. Their eggs are roundish, heavy, and of a whitish colour. The animal deposits them on the soil in little irregular heaps; at other times it deposits them one after the other, like the grains of a chaplet, in holes which it digs in the soil, or in the natural excavations created by moisture. The eggs are even found in the hollows of old trees; in fissures of walls or rocks.

When the young Helix issues from the egg, it is already provided with an extremely thin membranous shell. The timid and tender youth is conscious of its weakness and full of humility. It rarely trusts itself out of the obscure hole in which it was hatched; when it does, it is only at night, dreading the desiccating air, and, above all, the sun's rays, even with the house it always carries with it for shelter.

This calcareous and velluted house is spiral, which the animal has the inappreciable advantage of transporting without fatigue. It is light, and sometimes quite disproportionate to the body of the animal, which it covers only in that part which contains the viscera and respiratory organs. The form of the shell is generally much variegated. Some are flattened, others are orbicular or globose; in some the spiral is very pointed. The edges of the shell are sometimes simple, sharp, and pointed; others, on the contrary, thick and inverted, presenting an edging of great solidity.

The spire is generally rolled up from right to left. A helix shell, the spiral of which follows the inverse direction, that is, from left to right, is a rarity much sought after by amateurs.

The ancients held snails in especial esteem for the table. The Romans had many species served up at their feasts, which they distinguished in categories according to the delicacy of their flesh. Pliny tells us that the best were imported from Sicily, from the Balearic Isles, and from the Isle of Capri, the last dwelling-place of the aged Tiberius. The largest came from Illyria. Ships proceeded to the Ligurian coast to gather them for the tables of the Roman patricians. The great consumption led to the establishment of parks (Cochlearia, Varro; Cochlearum vivariá, Pliny), in order to fatten the animals, as is now done with oysters. They were fed for this end upon various plants mixed with soup; when it was desired to improve the flavour a little wine and sometimes laurel leaves were added. These parks were formed in humid shady places surrounded by a foss or a wall. Pliny has even transmitted to us the name of the inventor of the Cochleariæ, a certain Fulvius Hispinus. Addison describes with details one of these establishments kept up by the Capuchins at Fribourg in Switzerland, in imitation of the ingenious Roman gourmet we have named.

Among the Romans, snails were served at the funeral repast. Certain heaps of their shells, which are found in the cemetery of Pompeii, are the remains of those funeral festivities with which the inhabitants of the buried city honoured the tombs of their friends and relations.

The practice of eating snails had fallen into disuse in Europe when, in the seventeenth century, John Howard, the philanthropist, began to collect them with the view of reintroducing them as human food. He chose Helix Varronis, which was probably the species cultivated by the Romans; it surpasses all those of Europe in size, and was found plentifully in the district of Bagnes, in the Valois. Howard, having procured the species from Bagnes, found their increase so rapid that the crops were likely to be devoured by the swarms of molluscs thus brought together, and steps were at once taken to destroy them. In other parts of Europe the snail continues to be sought for as an article of luxury. They are consumed at Vienna in great numbers during Lent, supplies being brought from the Swiss canton of Appenzell. At Naples a soup made from Helix nemoralis is sold publicly to the strange population with which the streets of that city swarm, for the king's pavement is their bed-chamber, dining-saloon, and work-room. In France, snails are a valuable resource to the poor in the southern departments.

The flesh of all snails is not alike in a culinary point of view. Amateurs class as first in quality Helix vermicula, called at Montpelier the Little Hermit, because it buries itself so deeply in its shell. Helix aspersa (Figs. 193, 194, 195) is thought to be more tender and delicate. In Provence a species is called tapada, that is, "closed," from the cretaceous deposit with which it closes its shell.

In the north of France, and round Paris, Helix pomatia is the favourite culinary snail (Fig. 196). This is the species which is used as a speaking sign-board over the doors of the wine-shops and small restaurants in the neighbourhood of the Halles, at Paris. Its shell is globose and tun-shaped, very solid, marked with irregular transverse stripes of a brownish rust colour, with bands, often nearly effaced, of a deeper tint, and of the same colour. The animal is large, of a yellowish grey, and covered with elongated irregular tubercles.

Besides Helix pomatia, according to Moquin-Tandon, they eat in the north of France Helix sylvatica and H. nemoralis; at Montpelier, as we have already said, H. aspersa and H. rhodostoma; at Avignon, also, these, along with H. vermicula, are favourites. In Provence, Helix Pisana, with H. aspersa and melastoma, are preferred. At Bonifacio, Helix aspersa, H. vermicula, and, more rarely, H. rhodostoma; and in other localities the smaller species and young individuals of the larger kinds are employed for feeding poultry.

Certain species are also employed for feeding ducks. Thus, in the neighbourhood of Montpelier, ducks are fed upon Helix variabilis and H. rhodostoma. Some fishes, especially the young salmon, are very partial to the flesh of snails.

This very important genera is very numerous in species, which are distributed in groups according to the form of the shell; that is, whether it be globulous, as in Fig. 197, tun-bottomed, as in Fig. 198, plain or biform, as in Fig. 199, or truncated, as in Figs. 200 and 201. These figures will give the reader some idea of the multiplied and elegant forms which the shells of Helix sometimes assume.

In connection with the snails (Helix), we shall note some kindred genera which our space only permits us to name. Such is the genus Bulimus, the European species of which are numerous; some of them very small, others of medium size; of these, Bulimus sultanus (Figs. 204 and 205). In Figs. 206 and 207, the Berry Pupa (P. uva), as an example of another genus, is represented.

Yet another typical species may be noted, which is found abundantly amid the grass and shrubs near brooks round Paris and elsewhere. It is Succinea putris, presenting a small, thin, diaphanous shell of a pale amber yellow, marked with close and very fine longitudinal stripes (Fig. 208). The Achatina zebra of Chemnitz is a great snail, which devours shrubs and trees in Madagascar (Fig. 209). Finally, Vitrina, the shell of which is very small and very thin in some species—so small, indeed, in Vitrina fasciata (Fig. 210), that the animal cannot fully enter the shell—occupies a point of transition between Helix and Limax.

In the Pectinibranchial Gasteropods the gills are composed of numerous leaflets cut like the teeth of a comb, and attached, on one or many lines, to the upper part of the respiratory cavity. They constitute the most numerous order of Cephalous Molluscs, comprehending nearly all the univalve spiral shells, and many others which are simply conical. They inhabit the sea, rivers, and lakes, and are of all sizes. The most remarkable genera which we shall describe belong to the family of Trochoïdæ and Buccinoïdæ.

The fourth order of Gasteropods, Prosobranchiata, which includes the Pecteni Branchiata, is distinct in the sexes, has the branchiæ pectinated, and the mantle forms a vaulted chamber over the back of the head. It is divided into two sections and twenty-one families. The first section, Holostomata, contains the sea-snails. The first family we shall treat of is the Chitonidæ, containing Chitonellus and Chiton.

The Chitons are very singular creatures, destitute of eyes, of tentacles, and without jaws; they bear upon their back in place of a shell a cuirass composed of imbricated and movable scales. They have the power of elongating and contracting themselves like the snails. They roll themselves up into a ball like the woodlouse. They adhere with great force to the rocks, preferring those places most exposed to the beating waves. Chiton magnificus (Fig. 211) is widely distributed.

The second family, Dentaliadæ, affords the curious Dentalium, or tooth shell.

The Patellidæ, or Limpets, constitute a very numerous family, distinguished at once by the form and structure of the animal, and by that of the shell. Linnæus called it Patella, i. e., a deep dish or knee-cap.

The shells of the Patellidæ, our third family, are univalve, oval, or circular, non-spiral, but terminating in an elliptic cone, concave and simple beneath, non-pierced at the summit, entire and inclined anteriorly. They are smooth, or ornamented on the sides with ridges radiating from the summit, and often covered with scales; the edges are frequently dentate. The colours much varied. The interior is very smooth, and remarkable for the brilliancy and lustre of its tints.

The head of the animal is furnished with two pointed tentacles or horns, having an eye at the external base of each. The body is oval and nearly circular, conical, or depressed. The foot is in the form of a thick fleshy disk. Certain lamellar branchiæ are arranged in series all round the body.

The Limpets dwell upon the sea-shore, in the parts alternately covered and uncovered by the waves. They are almost always attached to rocks, or other submerged bodies, to which they adhere with great tenacity. If the common Limpet (Patella vulgata) is alarmed before any attempt is made to dislodge it, no human force, pulling in a direct line, can remove it, and it can sustain without being crushed a weight of many pounds. It holds on by the great quantity of vertical fibres of the foot, which in raising the median part forms in the centre a sort of sucker. It is the celebrated experiment of the Magdeburg cups which these little molluscs realise by their vital action.

These animals bury themselves in the chalky rocks to the depth of two or three lines; when they are dispersed, they are observed constantly to return to the same place. Their movements are, besides, extremely slow; the advance of the Limpet being only perceived by watching the slow upheaval of the shell above the plane of its position. It is supposed, from the mouth being armed on its upper edge with a large semi-lunar, horny, cutting tooth, and in its lower part from having a tongue furnished with horny hooks, and from their inhabiting in great numbers places covered with marine plants, that their food is chiefly vegetable.

The poorer inhabitants of the coast eat limpets when they have nothing else, but their flesh is singularly coriaceous and indigestible.

They are found in every sea; but are, however, found to be larger as well as more numerous, and much richer in colour, in Equatorial seas, and especially in the southern hemisphere, than in European seas. They attain, in fact, their maximum of development here; for in the Straits of Magellan species are found as large as a slop-basin, which the natives use for culinary purposes.

The common Limpet is thick, solid, oval, and nearly circular, generally conical, and covered with a great number of very fine stripes. Its colour is of a greenish grey, uniform above, and of a greenish yellow inside. It is abundant in the Channel and on Atlantic coasts.

The Blue Limpet, Patella cærulea (Fig. 212), from St. Helena, has an oval shell, broadest behind, moderately thick, depressed, flattened, covered with angular wrinkles, and dentate on the edge. It is of a spotted green outside and of a fine glossy blue within.

Other very elegant species are Patella umbella (Fig. 213), from the African coast. Patella granatina (Fig. 214), the ruby-eyed Limpet from the Antilles; Patella barbata, the bearded Limpet (Fig. 215); and the long spined Limpet, Patella longicosta (Figs. 216 and 217).

The fourth family, Calyptræidæ, types Pileopsis and Calyptræa, was classed by the older conchologists with Patella. Pileopsis Hungaricus, the Hungarian bonnet shell, is rather abundant on some parts of the British coast.

The fifth family, Fissurellidæ, contains Parmophorus, the duck's-bill-limpet of Australia, and Fissurella, the key-hole-limpet, which is remarkable for the opening of the apex of the shell.

The sixth family, Haliotidæ, contains Ianthina, Scissurella, and Haliotis.

The attention of naturalists has long been directed to a curious mollusc known under the name of Ianthina communis (Fig. 218); its body is globular, and it presents an opening in front without contracting itself in order to form the head, which is long and trumpet-shaped, terminating in a large buccal opening, furnished with horny plates, and covered with little hooks; and two conical tentacles, slightly contracted, but very distinct, each bearing at their external base a long peduncle. The foot is short, oval, divided into two parts: the anterior, concave and cup-shaped; the posterior, flat and fleshy. It is this foot, which bears a vesiculous mass like foam, which gives its peculiar character to the pretty mollusc. The mass consists of a great number of small bladders, which combine to keep the animal on the surface of the water. The shell is light, transparent, violet-coloured, and very much resembles the shell of the Helix. The Ianthinas inhabit the deep sea, and often form bands of very great extent. Messrs. Quoy and Gaimard have seen legions of Ianthinas driven by the current. They have sailed during many days through these wandering tribes, which would be the sport of every gale if they could not, by drawing their heads within their shells and contracting their natatorial vesicles, diminish their volume and increase their weight at will, so as to sink quietly to the bottom of the water till the tempest was over. The Ianthina possesses a liquid of a dark violet colour, which is believed by many naturalists to have been one of the purple dyes known to the ancients, if not the purple of Tyre: it is very common in the Mediterranean.

Haliotis, the ear-shell, is remarkable for its brilliant colours, and for a line of singular perforations in many of the species.

The seventh family, Turbinidæ, contains Trochus, Turbo, Protella, Monodonta, and Delphinula.

The genus Trochus are found in all seas, and near to the shore in the clefts of rocks, especially in places where sea-weeds grow luxuriantly. Some of these thick, cone-shaped shells are extremely beautiful, being richly nacred inside, and remarkable for the beauty and diversity of colour exhibited. Generally smooth, the great spiral is, nevertheless, sometimes edged with a series of regular spines. The form is conical, the spiral more or less raised, broad and angular at the base; the opening entire, depressed transversely, and the edge disunited in the upper part.

The animal which inhabits this shell is also spiral; its head is furnished with two conical tentacles, having at their base eyes borne on a peduncle; its foot is short, round at its two extremities, edged or fringed in its circumference, and furnished with a horny operculum, circular and regularly spiral.

The family is divided into many sub-genera. Among the Trochi, properly so called, we may notice Trochus niloticus (Fig. 219), T. virgatus (Fig. 220), T. inermis (Fig. 221), and T. Cookii (Fig. 222).

The genus Turbo are very generally diffused, being found on every shore, where they cling to rocks beaten by the waves. About fifty species are known, some of them large shells, others very small. Turbo margaritaceus (Fig. 225) is large, thick, and weighty, round-bellied, and deeply furrowed; in colour it is yellow, or rust-coloured, marked by square brown spots. Turbo argyrostomus, the Silver-mouthed Turbo (Fig. 226), is still larger, with protecting spines on the top of its larger spiral. Turbo marmoratus (Linnæus), the Marbled Turbo (Fig. 227), is the largest shell in the group. It is marbled, green, white, and brown, outside, and superbly nacred within. The Gold-mouthed Turbo is so named from its nacre being of a rich golden yellow. The Wavy Turbo (T. undulatus), (Fig. 228), vulgarly known as the Australian Serpent's Skin. The shell is white, ornamented with longitudinal waving flexible lines of spots of green, or greenish-violet. Turbo imperialis (Fig. 229), from the Chinese seas, is green without, and brilliantly nacred within; it is vulgarly known as the paroquet.

The Turbos are found in the North seas, in the Channel, and on the Atlantic coast. The animal is eaten in nearly all the sea-ports of the Channel.

Rotella Zealandica, from the Indian Ocean, whose shell, represented in Fig. 230, presents the most lively colours, forms one of a genus by no means numerous in species.

Near to the Trochi and Turbos in the system are the Monodonta.

The Monodonta are elegantly-marked shells, belonging to the seas of warm countries. M. Australis (Fig. 231) is a native of Australian seas. M. labia (Fig. 232) is a small brown shell, with white spots, which is very common on the shores of the Mediterranean.

The eighth family is Neritidæ, of which we give as types, Pileolus and Nerita. The hoof-shells, or Nerites, are numerous and pretty, and in external form approach Turbo.

Of the Delphinula only a small number of living species are known. They are natives of the Indian Ocean, and remarkable for their numerous spines and the asperity of their shell (Fig. 233).

The ninth family, Paludinidæ, contains Ampullaria, the idol snail of India, and the widely distributed Paludina.

Our tenth family, Littorinidæ, contains Solarium, and the periwinkles, Littorina and Phorus, example, P. Conchyliophorus (Fig. 224).

The genus Imperator belongs to the Turbinidæ, and as examples of it we may instance the Spurred Trochus, Imperator stella, which is studded with radiating spines (Fig. 234), and Imperator stellaris (Fig. 235); they are natives of the Australian seas. Imperator imperialis, vulgarly called the Royal Spur, and Trochus or Rotella Zealandica (Fig. 230), the New Zealand Spur, the spiral turns of which are sculptured in descending furrows, and studded with imbricated scales, which form a projecting edging round the margin of the shell, and give it a radiating form. This species is of a violet brown above and white below, and is still rare in collections.

The Sun-dial (Solarium), recognized by its deep umbilicus, wide and funnel-shaped, in the interior of which may be seen the little crenated teeth which follow the edge of every turn of the spiral up to the top. In most collections of these pretty shells we find the Staircase-shell (Solarium perspecticum) of Lamarck, from the Indian Ocean (Figs. 236, 237), the diameter of which is sometimes two inches and a half. The Australian Sun-dial (S. variegatum, Linnæus, Fig. 238) is another species frequently seen in collections: it is as much variegated above as below, of a white and rusty brown. The minute trellised Sun-dial, which is only ten lines in diameter, comes from the coast of Tranquebar.

The eleventh family, Turritellidæ, types Vermetus and Turritella, which last is a numerous family, being found in every sea. All these shells, as their name indicates, represent a winding pyramid, terminating in a sharp point, some of them having fluted spirals, others rounded, angular, or flat, and some of them elegantly pencilled. Figs. 239 to 243 represent some of the varied forms they assume.

The twelfth family, Melaniadæ, types, Paludomus and Melania, fresh-water genera.

The thirteenth family, Cerithiadæ, types, Aporrhais and Cerithium.

Cerithium is a marine shell, which is found in muddy bottoms, on ships, and more frequently at the mouths of rivers, but rarely beyond the point to which the tide reaches. The genus is numerous in species. Such are Cerithium fasciatum (Fig. 244) and Cerithium aluco (Fig. 245).

The Giant Cerithium, Cerithium giganteum (Fig. 246), is the living analogue of a magnificent fossil species belonging to the tertiary formation. The single known example of this species belongs to the Delessert Museum at Paris. A manuscript note by Lamarck, attached to this specimen, relates that this shell was first brought to Dunkirk in 1810 by an Englishman, one of the crew of an English ship. The English sailor had drawn it up from the bottom of the sea with the sounding-lead from a bed of rocks off the coast of Australia.

The fourteenth family, Pyramidellidæ, contains Chemnitzia and Pyramidella, extremely pointed shells.

The fifteenth family, Naticidæ, contains Lamellaria and Natica; the last of which is found in most seas.

The second section of the Prosobranchiata is termed Siphonostomata, which are characterized by a spiral imperforate shell, the animal of which has sometimes a horny operculum, and is furnished with an elastic trunk, the margin of the mantle acting as a siphon. They are carnivorous.

The first family is the Cypræidæ, containing the well-known Cypræa and Ovulum.

The Cowries, or Cypræa, are brilliant, smooth, and polished, oval-shaped, or oblong convex, with edges rolling inwards and longitudinal openings, narrow, arched, dentate on both edges, and notched at the extremities. The spiral, placed quite posteriorly, is very small, and often hidden by a calcareous bed of a vitreous appearance.

It is now known that the form and colouring of the shells vary very considerably, according to the age of the animal: so much so, indeed, that the same species examined at various stages of its growth would almost seem to belong to species and even to genera essentially different.

The young cowries are thin, conical, elongated; with conspicuous spiral, and large openings. The right edge soon becomes thicker, and folds itself inwardly; the opening is narrowed; finally, the spiral is unfolded in successive folds from the right edge, and by successive deposits of the vitreous matter we have spoken of the opening is gradually contracted, its extremities hollowed out, its edges disconnected, and the shell, until now only shaded in pale tints, assumes its most brilliant colours, disposed in bands or spots, as exhibited in Pl. XXII., in which Figs. I. and II. are the adult shells, and Fig. III. the young shell, of Cypræa Scottii.